Maintaining High Purity Gases; Using Metal Gas Lines; Removing Trapped Air - Micromeritics TriStar II 3020 Operator's Manual

TriStar II 3020
G. MAINTAINING HIGH PURITY GASES
The TriStar II 3020 was designed to accurately measure the surface area of all types of materials. It is
important that the gases (especially Krypton when using the Krypton option) used for these measure-
ments be of highest purity, especially when analyzing low surface area samples. Three ways to ensure
high purity gases are to always maintain:
• thoroughly purged gas pressure regulators
• non-permeable gas lines
• leak-free connections
Impure gas is strongly indicated, for example, if a series of measurements on a low surface area mate-
rial yields decreasing specific surface areas with decreasing quantities of sample. The TriStar uses very
small amounts of helium; therefore any residual air in the regulator can distort results of subsequent
analyses for quite some time.
Micromeritics offers the following suggestions to assist you in maintaining high purity gases (particu-
larly helium) for the TriStar.
• Use metal gas lines only
• Remove trapped air from the regulator and gas lines

Using Metal Gas Lines

You should always use metal gas lines which have been carefully cleaned of any oils and greases used
in the manufacturing process. Do not use plastic or rubber gas lines. When these types of permeable,
nonmetallic gas lines are used with helium, contaminants accumulate at a much faster rate. This causes
errors in analysis results and can also contaminate a clean sample.

Removing Trapped Air

When connecting the regulator to the gas bottle, air is unavoidably trapped on the high- and low-pres-
sure sides of the regulator, as well as in the gas lines. You should remove as much of this air as is
possible before opening the gas bottle valve. If this air is allowed to remain in the regulator, it will mix
with the helium and cause inaccurate results in subsequent analyses. Or if the valve is open for any
length of time, the air trapped on the high pressure side may diffuse back into the gas bottle and con-
taminate its entire contents.
There are two methods for removing trapped air from the regulator lines: the Purge Method and the
Evacuation Method.
302-42828-01 - Dec 2012
Appendix G
G-1